1. Technological Field
This technical disclosure pertains generally to isolating transmitting and receiving channels in a radio receiver front end, and more particularly to utilizing transistor circulators for isolating transmitter and receiver channels.
2. Background Discussion
Separating the transmitting and receiving channels connected to a single antenna is currently realized utilizing circulators which are often made of non-reciprocal magnetic material, such as ferrite. These circulators are not compatible with standard integrated circuit processing and can only provide suitable performance over a relatively narrow frequency band. Circulators based on optical links can provide broadband performance, however, they are also too physically bulky for integration on-chip.
As an alternative, active circulators based on transistor amplifiers have been developed, yet these add noise in the receiver and limit the maximum operating power of the transmitter.
A previous solution from the inventor (“Parametric conversion with distributed modulated capacitors (DMC) for low-noise and non-reciprocal RF front-ends”, S. Qin and Y. E. Wang, 2013 IEEE International Microwave Symposium, Seattle, June, 2013.) overcome the above problems, while it was limited to a maximum isolation of 13 dB over a broad bandwidth.
Accordingly, a need exists for a method and apparatus for separating the transmitting the receiving channels within a radio frequency front end which provides deeper levels of isolation and can be incorporated into integrated circuitry.